AIMS To describe the surveillance and epidemiology of sexually transmitted infections (STIs) in New Zealand. METHODS Sexual health clinics submitted STI data to the Institute of Environmental Science and Research (ESR). Infection rates were calculated by dividing the number of diagnoses by the number of total clinic visits. Because the denominator used to calculate infection rates changed in 1998, STI rates in 1998 cannot be directly compared with previous years and case numbers were used to identify recent trends. RESULTS In 1998, genital warts was the most commonly diagnosed STI (4.7%), followed by chlamydia (3.0%) and genital herpes (1.0%). Approximately two-thirds of gonorrhoea, chlamydia and genital warts diagnoses were in people aged less than 25 years. Chlamydia rates were 7.3% in Maori, 7.1% in Pacific Island people, and 2.1% in European. Gonorrhoea rates were 1.6% in Maori, 1.9% in Pacific Island people and 0.2% in European. The number of chlamydia and gonorrhoea cases increased between 1995 and 1998. CONCLUSIONS The reporting of data by age, sex and ethnicity has allowed a more useful evaluation of the incidence of STIs. The majority of STIs were diagnosed among young New Zealanders, and disproportionately high chlamydia and gonorrhoea infection rates were found among Maori and Pacific Island people.